Abstract

A natural superlattice (NSL) in siliconcarbide polytypes induces a miniband structure within the conduction band along the NSL axis C. It was found that the presence of NSL leads to an anisotropy of a nitrogen impurity impact ionization in SiC. For an electric field direction , the nitrogen impurity breakdown at temperature 4.2 K has not been observed up to the field 1.6 MV/cm for the polytype 6H-SiC. However, for the polytype 4H-SiC dependence breakdown field on impurity concentration demonstrates its usual behavior, which has also been observed for other semiconductor materials. Therewith, the impurity breakdown at the electric field perpendicular to the axis in 4H- and 6H-SiC demonstrates consistency with traditional conceptions. These results are explained theoretically.